Global climate modeling has had a long history. With constantly increasing
computing capacity, there is the opportunity for adding further complexity and
increasing horizontal resolution or decreasing the model grid boxes and the
number of vertical layers. Both are being considered and implemented by
scientists to make more realistic global climate models.
Transitioning to Earth System Modeling
So far, attempts to model the Earth System have been limited to a few key
components—the atmosphere, ocean, land, and sea ice. Some other components
like land ice have had to be neglected due to their complexity until now.
Recently, the National Center for Atmospheric
Research (NCAR) has released the Community Earth System Model (CESM), an
update of what they used to call the Community Climate System Model (CCSM).
The name change was largely motivated by the inclusion of a land ice
component.
The motivation to go towards Earth System modeling is the realization that
the various components are all important and highly integral. Of course, this
is not a new realization; this is why ocean, land, and sea ice components were
added to the atmosphere. Now, there is an increasing realization that life on
Earth also interacts with climate, that as the global climate is warming, the
various biomes or regions of unique combinations of plants and animals
are changing as well. They are moving poleward or even disappearing altogether.
This moves the climate change problem into a global change problem.
The modeling of such interactions needs an ecosystem dynamics model. CESM
has options to include a dynamic vegetation model, a model that actually grows
vegetation and the interaction between grass, trees, and shrubs, and a land
biogeochemistry model, a model that follows carbon and nitrogen through the
terrestrial biosphere (Oleson et al. 2010).
Another added complexity to global change modeling is the human component.
Humans are substantially changing the landscape with agriculture and urban
areas. Croplands have always been defined in climate models, but the
characteristics of such land are not constant. Farmers switch out different
crops or leave the land to fodder to recuperate nutrients, and in winter, there
is generally nothing grown. CESM also includes an option to include a transient
land cover prescription (Oleson et al. 2010).
In urban areas, buildings and roadways change the surface energy balance.
The fact that cities are warmer than the surrounding countryside is testimony
to this. CESM also includes an option to include an urban model which
simulates an "urban canyon" with a canyon floor that is divided into
components that represent roadways and lawns (Oleson et al. 2010).
The next step is to simulate the interactions of ocean biology with
climate. Such interactions would affect not only the carbon cycle but also the
energy balance in the ocean. Recent research has shown that the addition of
an ocean biogeochemistry model to an ocean GCM warmed SSTs and cooled
subsurface temperatures (Nobre et al. 2010, Manizza et al. 2005).
The Need for Increased Resolution
Another problematic feature of global climate models is that they do not
have sufficient horizontal and vertical resolution to capture certain weather
phenomena like hurricanes. Recent results modeling changes in hurricane
occurrence and intensity have been from using climate model simulations as a
boundary condition for smaller-scale models in a process known as
downscaling that accurately simulate hurricanes (e.g., Emanuel et al.
2008).
However if the resolution of global climate models can be increased
substantially, such processes can be then be simulated by the model. The
reason for this is the model grid boxes become small enough that physical
processes like convection become explicitly rather than implicitly treated.
A group of scientists at a recent meeting, the World Modelling Summit for
Climate Prediction (Shukla et al. 2009), had declared the need to increase
model resolution to properly simulate such processes. Downscaling to regional
model is not sufficient to capture the climate change of small-scale processes,
because such models cannot interact global-scale processes.
The Japanese have already had some success with very high-resolution global
modeling, but such a model has to use a building-sized supercomputer called the
Earth Simulator (Ohfuchi et al. 2007). Such results give us hope that with
improvements in computing technology, that such high-resolution modeling will
become more easily feasible on smaller-scale supercomputers in the future.
In conclusion, the future looks bright for global climate modeling with the
incorporation of more processes and increases in horizontal and vertical
resolution. Global climate modeling will remain an integral part of global
change research.
References
Emanuel, K., R. Sundararajan, J. Williams, 2008: Hurricanes and global
warming. Bulletin of the American Meteorological Society,
89, 347-367.
Manizza, M., C. Le Quéré, A. J. Watson, and E. T. Buitenhuis,
2005: Bio-optical feedbacks among phytoplankton, upper ocean physics and sea
ice in a global model. Geophysical Research Letters, 32,
L05603, doi:10.1029/2004GL020778.
Nobre, C., G. P. Brasseur, M. A. Shapiro, M. Lahsen, G. Brunet, A. J.
Busalacchi, K. Hibbard, S. Seitzinger, K. Noone, and J. P. Ometto, 2010:
Addressing the complexity of the Earth System. Bulletin of the American
Meteorological Society, 91, 1389-1396.
Ohfuchi, W., H. Sasaki, Y. Masumoto, and H. Nakamura, 2007:
"Virtual" atmospheric and oceanic circulation in the Earth Simulator.
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861-866.
Oleson, K. W., and 27 co-authors, 2010: Technical description of version
4.0 of the Community Land Model (CLM). NCAR Technical Note NCAR/TN-478+STR,
available at http://www.cesm.ucar.edu/models/cesm1.0/clm/CLM4_Tech_Note.pdf.
Shukla, J., R. Hagedorn, B. Hoskins, J. Kinter, J. Marotzke, M. Miller, T.
Palmer, and J. Slingo, 2009: Revolution in climate prediction is both
necessary and possible: A declaration at the World Modelling Summit for
Climate Prediction. Bulletin ofthe American Meteorological
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Shukla, J., T. N. Palmer, R. Hagedorn, B. Hoskins, J. Kinter, J. Marotzke,
M. Miller, and J. Slingo, 2010: Toward a new generation of world climate
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